JP2004241585A - Microstructure cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microstructure cleaning method capable of exfoliating/eliminating certainly unwanted substances such as a resist residual or the like without changing the property of a Low-k film and producing new contaminants, and further to provide a microstructure cleaned by the cleaning method. <P>SOLUTION: There is provided a cleaning method of eliminating unwanted substances attached to the microstructure by making a detergent composition containing essentially carbon dioxide, a detergent component for eliminating the unwanted substances, and a phase solution agent for dissolving the detergent component in the carbon dioxide, into a liquid under a high pressure to bring them into contact with the microstructure. Using fluoride denoted by a chemical formula N R<SP>1</SP>R<SP>2</SP>R<SP>3</SP>R<SP>4</SP>F as the detergent components, an operation is performed. In the formula, however, note that R<SP>1</SP>to R<SP>4</SP>are hydrogen or a hydrocarbon radical, while at least one of R<SP>1</SP>to R<SP>4</SP>is hydrogen or a methyl radical and besides at least one of R<SP>1</SP>to R<SP>4</SP>is the hydrocarbon radical with two or more carbon number. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２５】
上記表１から明らかな様に、洗浄成分としてＮ−Ｈ結合やＮ−ＣＨ_３結合を有するフッ化物を用いて洗浄した場合、Ｌｏｗ−ｋ膜へダメージを与えることなく、良好な洗浄性を得ることができる。しかし、これらのフッ化物を用いて洗浄すると、洗浄中に新たな汚染物質が生成していることが分かる。これに対し、洗浄成分としてＮ−Ｃ_４Ｈ_９結合を有するフッ化物を用いて洗浄した場合、洗浄中に新たな汚染物質は生成しないが、洗浄性が若干劣り、Ｌｏｗ−ｋ膜へのダメージも若干認められる。さらに、Ｎ−Ｃ_２Ｈ_５結合を有するフッ化物を用いて洗浄した場合、洗浄性の劣化およびＬｏｗ−ｋ膜へのダメージが認められると共に、洗浄中に新たな汚染物質も生成することが分かる。
【００２６】
表１に示した様に、フッ化物のＮに結合している置換基の種類に応じて、得られる結果が異なる理由は、ＮとＦ間におけるイオン結合力の差にあると本発明者らは考えた。即ち、フッ化物中のＮに結合している置換基が水素やメチル基であれば、ＮとＦ間のイオン結合力は強いので、非極性溶媒である二酸化炭素流体中であってもフッ化物は殆ど解離しない。このことにより、フッ化物が不要物質と効率良く結合して洗浄性が向上すると推測される。しかし、フッ化物と不要物質が結合して生成する新たな汚染物質は有機性が低く、二酸化炭素流体中に溶解し難いので、汚染物質は二酸化炭素流体中に残留したままとなる。
【００２７】
これに対し、フッ化物中のＮに結合している置換基がエチル基やブチル基の様に炭素数２以上の炭化水素であれば、ＮとＦ間のイオン結合力は弱いので、Ｎに結合している置換基が水素やメチル基のものよりも、非極性溶媒である二酸化炭素流体中で解離し易い。従って、フッ化物は不要物質と殆ど結合せず、洗浄性が劣化すると推測される。但し、二酸化炭素流体中で解離して生成する炭素数２以上の炭化水素基が不要物質と結合すると、新たな汚染物質が生成すると考えられるが、仮に汚染物質が生成したとしてもこの物質は有機性が高くなるので、二酸化炭素流体へは溶解し易くなる。そのため、二酸化炭素流体中に新たな汚染物質は生成しないと考えられる。
【００２８】
次に、本発明者らは、上記表１に示したフッ化物の代わりに、下記表２に示すヒドロキシ化合物とフッ化水素の混合物を洗浄成分として用いて半導体ウエハを洗浄し、同様の実験を行なった。実験結果を下記表２に併せて示す。
【００２９】
【表２】

【００３０】
上記表２から明らかな様に、ヒドロキシ化合物とフッ化水素の混合物を洗浄成分として用いても、得られる結果はフッ化物を洗浄成分として用いた場合と等しくなることが分かる。即ちヒドロキシ化合物とフッ化水素を混合することにより両者が反応し、上記表１に示したフッ化物と水が生成するからと考えられる。
【００３１】
そして、本発明者らがこれらの結果を基にさらに検討したところ、不要物質を除去するための洗浄成分として、下記（１）〜（３）に示すフッ化物または混合物を用いてやれば、Ｌｏｗ−ｋ膜の性状を変化させたり、新たな汚染物質を生成することなく、微細構造体からレジスト残渣等の不要物質を確実に剥離・除去できることを見出し、本発明を完成した。
【００３２】
（１）化学式ＮＲ^１Ｒ^２Ｒ^３Ｒ^４Ｆで示されるフッ化物
式中、Ｒ^１〜Ｒ^４は水素または炭化水素基であると共に、Ｒ^１〜Ｒ^４のうち少なくとも一つが水素またはメチル基であり、且つ、少なくとも一つが炭素数２以上の炭化水素基である
（２）化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とフッ化水素との混合物
式中、Ｒ^５〜Ｒ^８は水素または炭化水素基であると共に、Ｒ^５〜Ｒ^８のうち少なくとも一つが水素またはメチル基であり、且つ、少なくとも一つが炭素数２以上の炭化水素基である
（３）化学式ＮＲ^９Ｒ^１０Ｒ^１１で示されるアルキルアミンとフッ化水素との混合物
式中、Ｒ^９〜Ｒ^１１は水素または炭化水素基であり、且つ、Ｒ^９〜Ｒ^１１のうち少なくとも一つが炭素数２以上の炭化水素基である
【００３３】
以下、上記（１）〜（３）に示したフッ化物または混合物について詳述する。
【００３４】
（１）本発明の洗浄方法で用いる化学式ＮＲ^１Ｒ^２Ｒ^３Ｒ^４Ｆで示されるフッ化物とは、式中、Ｒ^１〜Ｒ^４は水素または炭化水素基であるが、Ｒ^１〜Ｒ^４のうち少なくとも一つが水素またはメチル基であると共に、少なくとも一つが炭素数２以上の炭化水素基である。
【００３５】
すなわち、Ｒ^１〜Ｒ^４のうち少なくとも一つが水素またはメチル基であることにより、ＮとＦ間のイオン結合力が強く、非極性溶媒である二酸化炭素流体中であってもフッ化物は殆ど解離しない。従って、フッ化物が不要物質と効率良く結合するので、洗浄性が向上する。このとき、Ｌｏｗ−ｋ膜へダメージも殆ど認められない。
【００３６】
但し、Ｒ^１〜Ｒ^４の全てが水素またはメチル基であると、化学式ＮＲ^１Ｒ^２Ｒ^３Ｒ^４Ｆで示されるフッ化物とＬｏｗ−ｋ膜等が反応して生成する汚染物質の有機性は乏しくなる。その結果、汚染物質は二酸化炭素へ溶解し難くなり、汚染物質が二酸化炭素流体中に残留することとなる。そこで、本発明の洗浄方法で用いるフッ化物は、Ｒ^１〜Ｒ^４のうち少なくとも一つを炭素数２以上の炭化水素基とすることが重要である。炭素数が多くなるほど有機性が高くなると共に、二酸化炭素流体中で解離し易くなる。このとき解離して生成する炭素数２以上の炭化水素基は、不要物質と結合して新たな汚染物質を生成すると考えられる。ところが、この汚染物質は有機性が高いので、二酸化炭素流体へ溶解して新たな汚染物質の生成を抑制できる。炭化水素基の炭素数は、好ましくは４以上であるが、炭素数が多くなり過ぎると、この物質自体が二酸化炭素へ溶解し難くなり、洗浄成分として作用しないので、炭化水素基の分子量は１００００以下とするのが好ましく、１０００以下とするのがより好ましい。なお、分子量が１００００の炭化水素基とは、直鎖状の炭化水素として計算した場合、炭素数は約７１４個となる。また、分子量が１０００の炭化水素基とは、直鎖状の炭化水素として計算した場合、炭素数は約７１個となる。炭化水素基は、エチル基やプロピル基の様な直鎖状のものに限定されず、例えば下記化学式で示す様な側鎖を有するものであっても構わない。
【００３７】
【化１】

【００３８】
化学式ＮＲ^１Ｒ^２Ｒ^３Ｒ^４Ｆで示されるフッ化物としては、例えばベンジルトリメチルアンモニウムフルオライド、ベンジルセチルジメチルアンモニウムフルオライド、セチルトリメチルアンモニウムフルオライド、ヘキシルトリメチルアンモニウムフルオライド、アセチルコリンフルオライド、トリエチルアミンハイドロフルオライド、トリブチルアミンハイドロフルオライドなどが好適に採用できる。
【００３９】
本発明の洗浄方法では、洗浄成分として上記（１）に示した化学式ＮＲ^１Ｒ^２Ｒ^３Ｒ^４Ｆで示されるフッ化物を用いる代わりに、（２）化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とフッ化水素との混合物または（３）化学式ＮＲ^９Ｒ^１０Ｒ^１１で示されるアルキルアミンとフッ化水素との混合物を用いても本発明の目的を達成できる。即ち化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とフッ化水素を混合するか、化学式ＮＲ^９Ｒ^１０Ｒ^１１で示されるアルキルアミンとフッ化水素を混合することにより、所望のフッ化物が生成するので、このフッ化物が洗浄成分として寄与するからある。なお、一般的にフッ化水素の取り扱いには、厳重な注意が必要であることが知られているが、本発明では、塩基性を示すヒドロキシ化合物またはアルキルアミンにフッ化水素を混合することによって中和され、安全性が高くなって取り扱い易くなる。
【００４０】
（２）本発明の洗浄方法で用いる化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とは、式中、Ｒ^５〜Ｒ^８は水素または炭化水素基であるが、Ｒ^５〜Ｒ^８のうち少なくとも一つが水素またはメチル基であると共に、少なくとも一つが炭素数２以上の炭化水素基である。Ｒ^５〜Ｒ^８をこの様に規定した理由は、上述したＲ^１〜Ｒ^４と同じである。
【００４１】
化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とフッ化水素との混合比は特に限定されないが、混合比（ヒドロキシ化合物／フッ化水素）がｍｏｌ比で１０を超えると、フッ化水素量が少ないためヒドロキシ化合物とフッ化水素が反応して生成するフッ化物量が少なくなる。その結果、洗浄力が低下するので、多量の洗浄成分を用いる必要があり、これに伴って相溶化剤の使用量が多くなる。そのため使用する溶媒が多くなって経済性に欠ける。この様な観点から、混合比は１０以下とするのが好ましく、１とするのが最も好ましい。但し、混合比が１より大きく下回るとフッ化水素量が多くなるため取り扱いが難しくなる。よって混合比は０．１以上とするのが好ましい。
【００４２】
なお、フッ化水素の取り扱い易さを考慮すると、高圧二酸化炭素流体に混合するフッ化水素量は０．５質量％以下とするのが好ましく、０．１質量％以下とするのがより好ましい。但し、本発明の洗浄方法において、ヒドロキシ化合物と混合するフッ化水素は、ガス状であっても液体状（フッ化水素酸）であっても構わない。
【００４３】
化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とフッ化水素を混合すると、化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８Ｆで示されるフッ化物が生成するが、このとき水も生成する。水が生成するとやはりＬｏｗ−ｋ膜へダメージを与えることがある。従って、水によるダメージを受けやすい洗浄対象物に対しては、洗浄成分として上記化学式ＮＲ^１Ｒ^２Ｒ^３Ｒ^４Ｆで示されるフッ化物を用いることが推奨される。しかし、上記フッ化物を用いるには、フッ化物を新たに合成する必要があるため、操作が煩雑となる。よって操作の簡便性を優先するのであれば、洗浄成分として上記化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物とフッ化水素の混合物を用いることが推奨される。
【００４４】
化学式ＮＲ^５Ｒ^６Ｒ^７Ｒ^８ＯＨで示されるヒドロキシ化合物としては、例えばベンジルトリメチルアンモニウムヒドロキシド、ベンジルセチルジメチルアンモニウムヒドロキシド、セチルトリメチルアンモニウムヒドロキシド、ヘキシルトリメチルアンモニウムヒドロキシド、アセチルコリンヒドロキシドなどが好適に採用できる。
【００４５】
（３）本発明の洗浄方法で用いる化学式ＮＲ^９Ｒ^１０Ｒ^１１で示されるアルキルアミンとは、式中、Ｒ^９〜Ｒ^１１は水素または炭化水素基であり、且つ、Ｒ^９〜Ｒ^１１のうち少なくとも一つが炭素数２以上の炭化水素基である。Ｒ^９〜Ｒ^１１をこの様に規定した理由は、上述したＲ^１〜Ｒ^４と同じである。
【００４６】
化学式ＮＲ^９Ｒ^１０Ｒ^１１で示されるアルキルアミンとフッ化水素との混合比は特に限定されないが、混合比（アルキルアミン／フッ化水素）がｍｏｌ比で１０を超えると、フッ化水素量が少ないためアルキルアミンとフッ化水素が反応して生成するフッ化物量が少なくなる。その結果、洗浄力が低下するので、多量の洗浄成分を用いる必要があり、これに伴って相溶化剤の使用量が多くなる。そのため多量の溶媒が必要となって経済性に欠ける。この様な観点から、混合比は１０以下とするのが好ましく、１とするのが最も好ましい。但し、混合比が１より大きく下回るとフッ化水素量が多くなるため取り扱いが難しくなる。よって混合比は０．１以上とするのが好ましい。
【００４７】
なお、フッ化水素の取り扱い易さを考慮すると、高圧二酸化炭素流体に混合するフッ化水素量は０．５質量％以下とするのが好ましく、０．１質量％以下とするのがより好ましい。但し、ヒドロキシ化合物と混合するフッ化水素は、ガス状であっても液体状（フッ化水素酸）であっても構わない。
【００４８】
化学式ＮＲ^９Ｒ^１０Ｒ^１１で示されるアルキルアミンとしては、例えばトリエチルアミンやトリブチルアミンなどが好適に採用できる。
【００４９】
上記フッ化物または混合物は、洗浄剤組成物１００質量％中、０．００１〜８質量％とすることが好ましい。洗浄能力を良好に発揮し得る前記フッ化物または混合物の量と、Ｌｏｗ−ｋ膜等のダメージを受けやすい膜に対するダメージをなるべく小さくするためには、上記範囲にする必要がある。８質量％を超えて存在させると、Ｌｏｗ−ｋ膜に対するダメージが避けられない。より好ましい上限は４質量％である。なお、Ｌｏｗ−ｋ膜に対するダメージとは、洗浄工程で洗浄剤組成物によってＬｏｗ−ｋ膜そのものがエッチングされて目減りすることを意味する。上記フッ化物または混合物は少ないほど、上記ダメージは小さくなるが、０．００１質量％以上存在していないと、洗浄に時間がかかるというデメリットがあるので、下限は０．００１質量％が好ましい。より好ましい下限は０．００５質量％である。
【００５０】
本発明の洗浄方法で用いる洗浄剤組成物としては、上記二酸化炭素および洗浄成分の他に相溶化剤を必須成分として含む。上記洗浄成分は二酸化炭素へ溶解し難いので、二酸化炭素に対する洗浄成分の溶解性を高めるために相溶化剤を用いる。従って、相溶化剤は、二酸化炭素と上記フッ化物または混合物の両方に溶解する化合物である。
【００５１】
相溶化剤としては、アルコールを用いることが好ましい。アルコールは、二酸化炭素に溶解し易く、またＬｏｗ−ｋ膜が形成されている微細構造体を洗浄する際に、アルコールがＬｏｗ−ｋ膜を保護するためＬｏｗ−ｋ膜と洗浄成分の反応を抑制する効果もある。さらにアルコールは、Ｌｏｗ−ｋ膜と洗浄成分が反応して生成する新たな汚染物質の溶解を促進し、ポリマー残渣の除去を促進する効果も認められる。
【００５２】
相溶化剤として用いるアルコールの具体例としては、メタノール、エタノール、ｎ−プロパノール、イソプロパノール、ｎ−ブタノール、イソブタノール、ジエチレングリコールモノメチルエーテル、ジエチレングリコールモノエチルエーテル、ヘキサフルオロイソプロパノール等が挙げられる。これらの相溶化剤のうち、洗浄成分を二酸化炭素へ溶解させる能力が高いという観点からエタノールが最も好ましい。
【００５３】
相溶化剤は、洗浄剤組成物１００質量％中、０．０１〜５０質量％とすることが好ましい。洗浄成分を二酸化炭素へ溶解させるためには、上記範囲にする必要があり、５０質量％を超えて相溶化剤を存在させると、多量に溶媒を必要とするため経済性に欠ける。より好ましい上限値は３０質量％である。一方、０．０１質量％以上存在していないと、洗浄成分を二酸化炭素へ溶解させることができないので、下限は０．０１質量％が好ましい。より好ましい下限値は１質量％である。
【００５４】
なお、洗浄成分を二酸化炭素へ効率良く溶解させるには、相溶化剤を洗浄成分の量に対して質量基準で５倍程度混合することが好ましい。即ち、相溶化剤の量は、洗浄成分の量に応じて上記範囲内で調整することが推奨される。
【００５５】
以上のように本発明の洗浄方法で用いることのできる洗浄剤組成物は、二酸化炭素と洗浄成分（上記フッ化物または混合物）と相溶化剤を必須的に含むものであるが、本発明の目的を損なわない範囲で他の化合物（例えば、プロピレングリコールなど）が含まれていてもよい。
【００５６】
次に、上記洗浄剤組成物を用いて微細構造体を洗浄するための具体的な方法を図面を用いて説明する。図１は、本発明の洗浄方法を実施するための洗浄装置の一例である。図１中、１は二酸化炭素ボンベ、２は二酸化炭素送給ポンプ、３は洗浄成分タンク、４は洗浄成分送給ポンプ、５は切り替えバルブ、６はリンス成分タンク、７はリンス成分送給ポンプ、８は切り替えバルブ、９は高圧容器、１０は恒温槽、１１は圧力調整弁、１２は流量計である。この図１では、洗浄成分としてベンジルトリメチルアンモニウムフルオライドとアルコールの混合液を供給する方法を採用しており、洗浄成分タンク３には、ベンジルトリメチルアンモニウムフルオライドとアルコールの混合液が、リンス成分タンク６にはアルコールが貯蔵されているものとする。なお、洗浄成分タンク３にはベンジルトリメチルアンモニウムフルオライドのみを貯蔵しておき、アルコールは必要に応じてリンス成分タンク６から別途供給するように構成してもよい。
【００５７】
図１の装置で洗浄工程を実施する際には、まず、洗浄対象物（微細構造体）を高圧容器９の中に入れる。次いで、二酸化炭素ボンベ１から、ポンプ２で二酸化炭素を高圧容器９へと供給して圧力を調整しながら、恒温槽１０により高圧容器９を所定の温度に設定する。なお、恒温槽１０に代えて、高圧容器９として加熱装置付きのものを用いても良い。
【００５８】
次いで、洗浄成分（ベンジルトリメチルアンモニウムフルオライドとアルコールの混合液）を洗浄成分タンク３から、ポンプ４を用いて高圧容器９へ導入することにより、洗浄工程が始まる。このとき、二酸化炭素、洗浄成分の送給は、連続的に行うものでも、所定の圧力に達した段階で送給を止める（あるいは送給を止めて循環させる）バッチ式であっても、いずれでも良い。
【００５９】
洗浄工程は、２０〜１２０℃で行う。２０℃よりも低いと、洗浄が終了するのに時間がかかり、効率が低くなる。超臨界二酸化炭素とするのであれば３１℃以上とする。１２０℃を超えても洗浄効率の向上が認められない上、エネルギー的に無駄である。より好ましい温度の上限は１００℃、さらに好ましい上限は８０℃である。圧力は、５〜３０ＭＰａが好ましく、より好ましくは７．１〜２０ＭＰａで行うとよい。洗浄に要する時間は、洗浄対象物の大きさや不要物質の量等に応じて適宜変更すればよいが、洗浄に長時間かけるとＬｏｗ−ｋ膜のダメージが大きくなる上に、効率的でないため、一般的なウエハ１枚であれば３分以下が好ましく、２分以下がより好ましい。
【００６０】
洗浄を行った後は、リンス工程を行う。リンス工程では、レジスト残渣等が混在する洗浄後の溶液を、いきなり二酸化炭素のみと混合すると、不要物質が析出したり、洗浄工程で生じたパーティクルが微細構造体表面に残存することが考えられるため、まず二酸化炭素とアルコールとの混合物による第１リンス工程を行う。洗浄工程から第１リンス工程切り替え時に、高圧容器９内でバックミキシングによって液組成が変化し得る可能性があるが、アルコールと二酸化炭素の混合物を第１リンス液として用いると、この液組成変化を少なくでき、溶解度の変化を小さくできるため、洗浄成分の析出等の不都合を回避することができる。この点で、洗浄成分に混合したアルコールと、リンス工程で用いるアルコールは同じアルコールを用いることが好ましい。
【００６１】
第１リンス工程では、洗浄成分の送給を切り替えバルブ５によって止め、代わりに切り替えバルブ８を開けて、リンス成分（アルコール）をリンス成分タンク６から、ポンプ７を用いて高圧容器９へ導入しながら、導入量に応じて（流量計１２をチェックしても良い）、洗浄後の溶液を高圧容器９から導出させればよい。またこの工程中、切り替えバルブ８を用いて、徐々にまたは段階的に、リンス成分（アルコール）の送給量を低減させ、最終的には二酸化炭素のみを高圧容器９に充填させる（第２リンス工程）ようにすることが好ましい。乾燥が容易だからである。洗浄工程およびリンス工程で導出された液体は、例えば気液分離装置等からなる二酸化炭素回収工程において、ガス状二酸化炭素と、液状成分とに分離できるので、各成分を回収して再利用が可能である。
【００６２】
リンス工程終了後は、圧力調整弁１１によって、高圧容器９の内部を常圧にすると、二酸化炭素は、ほとんど瞬時に気体になって蒸発するので、基板等の洗浄対象物は、その表面にシミ等が生じることもなく、また、微細パターンが破壊されることもなく、乾燥する。
【００６３】
なお、上記図１の装置は、最も簡単な構成の例であり、公知の手段で装置構成を変えても構わない。
【００６４】
【実施例】
以下、本発明を実施例によって更に詳細に説明するが、下記実施例は本発明を限定する性質のものではなく、前・後記の趣旨に適合し得る範囲で適当に変更して実施することも可能であり、それらはいずれも本発明の技術的範囲に含まれる。
【００６５】
Ｓｉウエハ上に、スピンオン方式で、有機シリコーン系ＭＳＱ原料を塗布・加熱して、ＭＳＱ系ポーラスＬｏｗ−ｋ膜を形成した。その上にＡｒＦ用のフォトレジストによってパターンを作り、露光・現像して、ラインとスペース（幅１３０ｎｍ）が交互に現れるレジストパターンと、約１０μｍ角の広幅のパターンからなるウエハサンプルを作製した。このウエハサンプルをフッ素系ガスでエッチングしてＬｏｗ−ｋ膜にパターンを作った後、水素プラズマでアッシング処理を施してレジストの除去を行った。アッシング処理後にウエハ表面を走査型電子顕微鏡で５００００倍で観察したところ、レジストが塗布されていたライン上と、広幅パターンの上にレジスト残渣が認められた。レジスト残渣が認められたウエハを、前記図１に示した装置を用いて洗浄した。洗浄の手順および洗浄条件を図面を用いて説明する。
【００６６】
図１に示した装置を用いて、このアッシング処理後のサンプルを高圧容器９の中へ置き、高圧容器９の蓋を閉じ、二酸化炭素ボンベ１からポンプ２で二酸化炭素を高圧容器９へと供給して、圧力を１５ＭＰａに調整しながら、恒温槽１０により高圧容器９を５０℃に保持した。ついで、洗浄成分と相溶化剤を表３に示した組成に混合したものを、洗浄成分タンク３からポンプ４を用いて高圧容器９へと導入し、高圧容器９の内部が１５ＭＰａになるように圧力調整弁の開閉を行った。洗浄工程を１分間行い、次いで洗浄成分として用いたものと同じ相溶化剤（５質量％）と二酸化炭素による第１リンス工程と、二酸化酸素のみの第２リンス工程を行った後、ポンプ２を停止し、圧力調整弁１１を開けて高圧容器９内の圧力を常圧に戻し、ウエハを取り出した。
【００６７】
なお、表３中、ＭｅＯＨはメタノールを、ＥｔＯＨはエタノールを、ＩＰＡはイソプロパノールを夫々表し、これらの相溶化剤量は、洗浄剤組成物１００質量％のうちのＣＯ_２および上記フッ化物または混合物以外の残部である。
【００６８】
【表３】

【００６９】
洗浄によるレジスト残渣の除去度合い（洗浄性）と、Ｌｏｗ−ｋ膜のダメージ（洗浄前後におけるラインパターン幅の変化量）と、洗浄中にＬｏｗ−ｋ膜等と洗浄成分が反応して新たな汚染物質が生じたか否かを、走査型電子顕微鏡で５００００倍で観察し、下記基準で判断して結果を表４に示した。
【００７０】
［レジスト残渣の除去度合い（洗浄性）］
○：残渣がどこにも認められない
△：ライン上または広幅パターン上のどちらかに残渣が一部認められる
×：いずれの残渣も除去されていない
［Ｌｏｗ−ｋ膜のダメージ］
○：洗浄前に比べてライン幅の変化が５％未満の減少に留まっている
△：洗浄前に比べてライン幅の変化が５％以上減少しているが、パターンは倒れていない
×：洗浄中に洗浄成分によるエッチングが進みすぎて、ラインパターンが倒壊している
［新たな汚染物質の生成の有無］
○：新たな汚染物質は生成していない
△：ライン上または広幅パターン上に残渣が認められる
×：ライン上および広幅パターン上に残渣が認められる
【００７１】
【表４】

【００７２】
表３及び表４から次の様に考察できる。Ｎｏ．１〜１７は本発明で規定する要件を満足する本発明例であり、Ｌｏｗ−ｋ膜の性状を変化させたり、新たな汚染物質を生成することなく、レジスト残渣等の不要物質を確実に剥離・除去できている。但し、Ｎｏ．１５は、ヒドロキシ化合物とフッ化水素の混合比が、ｍｏｌ比で１０を超えているので、洗浄性が若干劣る。一方、Ｎｏ．１８〜２１は、本発明で規定する何れかの要件を満足しない比較例であり、所望の効果が得られていない。
【００７３】
【発明の効果】
本発明によれば、微細構造体を洗浄するに際して、Ｌｏｗ−ｋ膜の性状を変化させたり、新たな汚染物質を生成することなく、レジスト残渣等の不要物質を確実に剥離・除去できる微細構造体の洗浄方法、および、該洗浄方法でによって洗浄された微細構造体を提供することができる。
【図面の簡単な説明】
【図１】本発明の洗浄方法を実施するための洗浄装置の一例を示す説明図である。
【符号の説明】
１ 二酸化炭素ボンベ
２ 二酸化炭素送給ポンプ
３ 洗浄成分タンク
４ 洗浄成分送給ポンプ
５ 切り替えバルブ
６ アルコールタンク
７ アルコール送給ポンプ
８ 切り替えバルブ
９ 高圧容器
１０ 恒温槽
１１ 圧力調整弁
１２ 流量計[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cleaning method for a structure having fine irregularities (fine structure surface) such as a semiconductor wafer, and for example, relates to a cleaning method for separating and removing a resist residue and the like from a semiconductor wafer in a semiconductor manufacturing process. It is.
[0002]
[Prior art]
In a semiconductor manufacturing process, a step of forming a pattern using a resist is often used, but after etching, the unnecessary resist after serving a role of masking is ashed (ashed) by oxygen plasma or the like. (Ashing step). After the ashing step, a cleaning step is required for removing and removing unnecessary substances such as residues in the etching step and resist residues that could not be removed in the ashing step from the wafer surface. This cleaning step is an important step frequently performed in the semiconductor manufacturing process, not only after the ashing step.
[0003]
In recent years, in the cleaning process, the use of liquefied or supercritical (hereinafter, referred to as “high pressure”) carbon dioxide having low viscosity and excellent osmotic power as a medium for a cleaning liquid or a rinsing liquid has been studied. Compared to wet cleaning using water as a medium, high-pressure carbon dioxide has a high cleaning effect due to its excellent penetration between fine patterns, and can be dried without creating a gas-liquid interface, so that patterns can be formed by capillary force. There is no risk of overthrowing.
[0004]
However, although high-pressure carbon dioxide functions as a low-viscosity solvent, it does not have sufficient dissolving power for unnecessary substances, and the cleaning power alone is insufficient. Therefore, the present inventors have invented a method of adding a basic substance as a cleaning component to high-pressure carbon dioxide, and adding an alcohol as a compatibilizer for dissolving the basic substance and the like, and performing a cleaning method. (See Patent Documents 1 and 2). However, as a result of further studies by the present inventors, a semiconductor wafer having a low dielectric constant interlayer insulating film (Low-k film), which has been widely used recently, or a semiconductor wafer having a process rule of 130 nm or less is used. In the case of cleaning using a high-pressure carbon dioxide fluid containing a basic substance, unnecessary substances such as resist residues may not be sufficiently removed or removed. Also, if a large amount of basic substance is mixed with a high-pressure carbon dioxide fluid to increase the cleaning power, the properties of the Low-k film are changed, and the low-k film and unnecessary substances react with the basic substance to cause new contamination. It has been found that a substance is generated and causes deterioration of the quality of the semiconductor wafer. The problem that the quality of the semiconductor wafer is deteriorated occurs more frequently as the cleaning component has a higher ability to remove unnecessary substances such as resist residues. This is because the cleaning component (basic substance) etches the Low-k film having a configuration similar to that of the resist residue, thereby damaging the Low-k film and changing the shape of the fine pattern. Conceivable.
[0005]
By the way, in a cleaning process, it is known to use hydrogen fluoride as a cleaning component. However, strict attention is required for handling hydrogen fluoride, and the operation becomes complicated.
[0006]
[Patent Document 1]
JP-A-2002-237481 (see "Claims")
[Patent Document 2]
U.S. Patent Application Publication No. 2002 / 0164873A (see "Claims")
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of such a situation, and an object thereof is to change the properties of a Low-k film or to generate new contaminants when cleaning a microstructure. An object of the present invention is to provide a method for cleaning a fine structure capable of reliably peeling and removing unnecessary substances such as a resist residue, and a fine structure cleaned by the cleaning method.
[0008]
[Means for Solving the Problems]
The method for cleaning a microstructure according to the present invention that can solve the above-mentioned problems includes a carbon dioxide, a cleaning component for removing unnecessary substances, and a compatibilization for dissolving the cleaning component in the carbon dioxide. A cleaning method for removing unnecessary substances adhering to the microstructure by bringing a cleaning composition essentially containing an agent into fluid under high pressure and contacting the microstructure, wherein the cleaning method comprises: As a component, the chemical formula NR ¹ R ² R ³ R ⁴ The point is that the fluoride represented by F is used.
[0009]
However, in the formula, R ¹ ~ R ⁴ Is a hydrogen or hydrocarbon group, and R ¹ ~ R ⁴ At least one is a hydrogen or methyl group, and at least one is a hydrocarbon group having 2 or more carbon atoms.
[0010]
The above object is to form a fluid under a high pressure into a cleaning composition essentially containing carbon dioxide, a cleaning component for removing unnecessary substances, and a compatibilizer for dissolving the cleaning component in the carbon dioxide. A cleaning method for removing unnecessary substances attached to the fine structure by contacting the fine structure with the fine structure, wherein the cleaning component is a chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ The problem can also be solved by using a mixture of a hydroxy compound represented by OH and hydrogen fluoride.
[0011]
However, in the formula, R ⁵ ~ R ⁸ Is a hydrogen or hydrocarbon group, and R ⁵ ~ R ⁸ At least one is a hydrogen or methyl group, and at least one is a hydrocarbon group having 2 or more carbon atoms.
[0012]
In addition, the above-mentioned problem, carbon dioxide, a cleaning component for removing unnecessary substances, and a cleaning composition essentially containing a compatibilizer for dissolving the cleaning component in the carbon dioxide, under high pressure, A cleaning method for removing unnecessary substances attached to the microstructure by making the fluid into contact with the microstructure, wherein the cleaning component is a chemical formula NR ⁹ R ¹⁰ R ¹¹ Can also be solved by using a mixture of an alkylamine represented by the formula (1) and hydrogen fluoride.
[0013]
However, in the formula, R ⁹ ~ R ¹¹ Is a hydrogen or hydrocarbon group, and R ⁹ ~ R ¹¹ At least one of them is a hydrocarbon group having 2 or more carbon atoms.
[0014]
It is preferable to use an alcohol as the compatibilizer. The concentration of the cleaning component in the cleaning composition is preferably 0.001 to 8% by mass. Further, the mixing ratio of the hydroxy compound or the alkylamine to hydrogen fluoride (hydroxy compound or alkylamine / hydrogen fluoride) is preferably 0.1 to 10 in terms of mol ratio.
[0015]
Note that the present invention also includes a microstructure cleaned by the cleaning method of the present invention.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The object of the cleaning method of the present invention is a fine structure, for example, a semiconductor wafer to which unnecessary substances such as a resist residue after ashing are attached in the vicinity of fine irregularities.
[0017]
It is considered that the resist residue consists of a resist polymer that has been converted into an inorganic polymer through an ashing process, a resist polymer that has been modified by fluorine in an etching gas, or a modified product such as polyimide used for an antireflection film. The method of the present invention is suitable for removing such a resist residue after ashing. Of course, the cleaning method of the present invention is not limited to the case where the resist residue is removed, and is also applicable to the case where a substance to be removed other than the resist residue exists on the semiconductor wafer in the semiconductor wafer manufacturing process. . For example, the cleaning method of the present invention is also applicable when removing a resist before ashing or a resist after implantation, or removing a residue after CMP existing as fine projections on a flat wafer surface from a semiconductor wafer surface. Can be suitably used.
[0018]
The cleaning method of the present invention is particularly preferably applied to a semiconductor wafer on which a film easily damaged in a cleaning step such as a Low-k film is formed. Applicable Low-k films include hybrid-type MSQ (methylsilsesquioxane) -based Low-k films (for example, “JSR LKD” series of JSR Corporation), and Si-based Low-k films by CVD. For example, "Black Diamond" of Applied Materials, etc., an organic Low-k film (for example, "SiLK" (registered trademark) of Dow Chemical Company, "FLARE" (registered trademark) of Honeywell) and the like can be mentioned. Can be The Low-k film may be any one formed by a spin-on method, one formed by a CVD method, or the like. Further, the porous membrane (porous type) can be preferably applied because the cleaning method of the present invention does not leave any impurities in the pores. Note that the cleaning method of the present invention can also be applied to a semiconductor wafer on which such a film that is easily damaged is not formed.
[0019]
Further, the fine structure to be cleaned by the cleaning method of the present invention is not limited to a semiconductor wafer, and a fine pattern is formed on the surface of various base materials such as metal, plastic, and ceramics, and a substance to be removed is required. If the object to be cleaned is such that it adheres or remains on its surface, it can be the object of the cleaning method of the present invention.
[0020]
The cleaning method of the present invention considers that the cleaning power is insufficient only with a high-pressure carbon dioxide fluid, and a cleaning component for removing unnecessary substances, and for dissolving the cleaning component in the carbon dioxide. A cleaning composition essentially containing a compatibilizer and formed into a fluid under high pressure is used as a cleaning medium.
[0021]
Here, carbon dioxide is used as a high-pressure fluid because the diffusion coefficient is high and dissolved unnecessary substances can be easily dispersed in a medium. In such a case, it has a property intermediate between the gas and the liquid, so that it can more easily penetrate into the fine concave portions. High pressure means 5 MPa or more, and a supercritical carbon dioxide fluid may be at a critical temperature (31 ° C.) or more and a critical pressure (7.1 MPa) or more. However, if the pressure is 5 MPa or more and the temperature is 20 ° C. or more, carbon dioxide becomes a gaseous fluid and shows a sufficient osmotic power as a cleaning medium.
[0022]
As described above, the present inventors have already invented a method of adding a basic substance as a cleaning component to high-pressure carbon dioxide, and adding an alcohol as a compatibilizer for dissolving the basic substance in high-pressure carbon dioxide and performing a cleaning method. Then, the application was filed as Patent Documents 1 and 2. However, as a result of further studies, it was found that (1) it was not possible to sufficiently remove and remove unnecessary substances such as resist residues, (2) the properties of the low-k film changed, and (3) the low-k film. It has been found that the reaction between unnecessary substances and the basic substance and the generation of new contaminants causes deterioration of the quality of the semiconductor wafer.
[0023]
Therefore, the semiconductor wafer on which the Low-k film was formed was washed using a fluid in which fluoride shown in Table 1 below was added to high-pressure carbon dioxide as a cleaning component and alcohol (ethanol) was added as a compatibilizer. Of unnecessary substances at the time (cleanability), damage to the Low-k film (change in line pattern width before and after cleaning), and whether a cleaning component reacts with the Low-k film or the unnecessary substances to generate new contaminants. It was evaluated by observing at a magnification of 50,000 with a scanning electron microscope. The evaluation results are shown in Table 1 below. The detailed experimental procedures and evaluation criteria are the same as those in the examples described later.
[0024]
[Table 1]

[0025]
As is clear from Table 1 above, N--H bonds and N--CH ₃ When cleaning is performed using a fluoride having a bond, good cleaning properties can be obtained without damaging the Low-k film. However, when cleaning is performed using these fluorides, it is found that new contaminants are generated during cleaning. On the other hand, N-C ₄ H ₉ When cleaning is performed using a fluoride having a bond, no new contaminants are generated during the cleaning, but the cleaning property is slightly inferior, and damage to the Low-k film is slightly recognized. Further, N-C ₂ H ₅ When cleaning is performed using a fluoride having a bond, deterioration of the cleaning property and damage to the Low-k film are recognized, and it is also found that new contaminants are generated during the cleaning.
[0026]
As shown in Table 1, the inventors of the present invention attributed to the difference in the ionic bonding force between N and F that the obtained results differed depending on the type of the substituent bonded to N of the fluoride. Thought. That is, if the substituent bonded to N in the fluoride is hydrogen or a methyl group, the ionic bond between N and F is strong, so that the fluoride can be used even in a carbon dioxide fluid which is a nonpolar solvent. Hardly dissociates. It is presumed that, by this, the fluoride is efficiently bonded to the unnecessary substance and the cleaning property is improved. However, the new contaminants generated by the combination of the fluoride and the unnecessary substances have low organicity and are hardly dissolved in the carbon dioxide fluid, so that the contaminants remain in the carbon dioxide fluid.
[0027]
On the other hand, if the substituent bonded to N in the fluoride is a hydrocarbon having 2 or more carbon atoms, such as an ethyl group or a butyl group, the ionic bond between N and F is weak. It is more easily dissociated in carbon dioxide fluid, which is a non-polar solvent, than when the substituents bonded are hydrogen or methyl groups. Therefore, it is presumed that the fluoride hardly binds to the unnecessary substance and the cleaning property is deteriorated. However, if a hydrocarbon group having 2 or more carbon atoms generated by dissociation in a carbon dioxide fluid is combined with an unnecessary substance, it is considered that a new pollutant is generated. The solubility in the carbon dioxide fluid is increased. Therefore, it is considered that no new pollutants are generated in the carbon dioxide fluid.
[0028]
Next, the present inventors cleaned a semiconductor wafer using a mixture of a hydroxy compound and hydrogen fluoride shown in Table 2 below as a cleaning component instead of the fluoride shown in Table 1 above, and carried out a similar experiment. Done. The experimental results are shown in Table 2 below.
[0029]
[Table 2]

[0030]
As is clear from Table 2 above, even when a mixture of a hydroxy compound and hydrogen fluoride is used as a cleaning component, the obtained results are equal to those obtained when fluoride is used as a cleaning component. That is, it is considered that by mixing the hydroxy compound and hydrogen fluoride, they react with each other to generate the fluoride and water shown in Table 1 above.
[0031]
The present inventors have further studied based on these results. As a cleaning component for removing unnecessary substances, the following fluorides or mixtures shown in (1) to (3) are used. The inventors have found that unnecessary substances such as a resist residue can be reliably removed and removed from the fine structure without changing the properties of the -k film or generating new contaminants, and completed the present invention.
[0032]
(1) Chemical formula NR ¹ R ² R ³ R ⁴ Fluoride represented by F
Where R ¹ ~ R ⁴ Is a hydrogen or hydrocarbon group, and R ¹ ~ R ⁴ At least one is a hydrogen or methyl group, and at least one is a hydrocarbon group having 2 or more carbon atoms
(2) Chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ Mixture of hydroxy compound represented by OH and hydrogen fluoride
Where R ⁵ ~ R ⁸ Is a hydrogen or hydrocarbon group, and R ⁵ ~ R ⁸ At least one is a hydrogen or methyl group, and at least one is a hydrocarbon group having 2 or more carbon atoms
(3) Chemical formula NR ⁹ R ¹⁰ R ¹¹ Mixture of alkylamine and hydrogen fluoride represented by
Where R ⁹ ~ R ¹¹ Is a hydrogen or hydrocarbon group, and R ⁹ ~ R ¹¹ At least one of which is a hydrocarbon group having 2 or more carbon atoms
[0033]
Hereinafter, the fluorides or mixtures shown in the above (1) to (3) will be described in detail.
[0034]
(1) Chemical formula NR used in the cleaning method of the present invention ¹ R ² R ³ R ⁴ The fluoride represented by F is represented by the formula: ¹ ~ R ⁴ Is a hydrogen or hydrocarbon group, but R ¹ ~ R ⁴ At least one is a hydrogen or methyl group, and at least one is a hydrocarbon group having 2 or more carbon atoms.
[0035]
That is, R ¹ ~ R ⁴ If at least one of them is a hydrogen or a methyl group, the ionic bond between N and F is strong, and the fluoride hardly dissociates even in a carbon dioxide fluid which is a nonpolar solvent. Therefore, the fluoride is efficiently bonded to the unnecessary substance, so that the cleaning property is improved. At this time, the Low-k film is hardly damaged.
[0036]
Where R ¹ ~ R ⁴ Are all hydrogen or methyl groups, the chemical formula NR ¹ R ² R ³ R ⁴ The contaminant generated by the reaction between the fluoride represented by F and the Low-k film or the like becomes less organic. As a result, the contaminants are less likely to dissolve in the carbon dioxide, and the contaminants remain in the carbon dioxide fluid. Therefore, the fluoride used in the cleaning method of the present invention is R ¹ ~ R ⁴ It is important that at least one of them is a hydrocarbon group having 2 or more carbon atoms. The higher the carbon number, the higher the organicity and the easier it is to dissociate in the carbon dioxide fluid. At this time, the hydrocarbon group having 2 or more carbon atoms generated by dissociation is considered to combine with an unnecessary substance to generate a new pollutant. However, since this pollutant is highly organic, it can be dissolved in a carbon dioxide fluid to suppress the generation of new pollutants. The number of carbon atoms of the hydrocarbon group is preferably 4 or more. If the number of carbon atoms is too large, the substance itself becomes difficult to dissolve in carbon dioxide and does not act as a cleaning component. Therefore, the molecular weight of the hydrocarbon group is 10,000. It is preferably at most 1,000, more preferably at most 1,000. Note that a hydrocarbon group having a molecular weight of 10,000 has about 714 carbon atoms when calculated as a linear hydrocarbon. Further, a hydrocarbon group having a molecular weight of 1000 has about 71 carbon atoms when calculated as a linear hydrocarbon. The hydrocarbon group is not limited to a linear group such as an ethyl group or a propyl group, and may have, for example, a side chain represented by the following chemical formula.
[0037]
Embedded image

[0038]
Chemical formula NR ¹ R ² R ³ R ⁴ Examples of the fluoride represented by F include benzyltrimethylammonium fluoride, benzylcetyldimethylammonium fluoride, cetyltrimethylammonium fluoride, hexyltrimethylammonium fluoride, acetylcholine fluoride, triethylamine hydrofluoride, tributylamine hydrofluoride and the like. Can be suitably adopted.
[0039]
In the cleaning method of the present invention, the chemical formula NR shown in the above (1) is used as a cleaning component. ¹ R ² R ³ R ⁴ Instead of using a fluoride represented by F, (2) a chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ A mixture of a hydroxy compound represented by OH and hydrogen fluoride or (3) a chemical formula NR ⁹ R ¹⁰ R ¹¹ The object of the present invention can also be achieved by using a mixture of an alkylamine represented by the formula (1) and hydrogen fluoride. That is, the chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ A hydroxy compound represented by OH is mixed with hydrogen fluoride, or a compound of the formula NR ⁹ R ¹⁰ R ¹¹ This is because a desired fluoride is generated by mixing the alkylamine represented by (1) with hydrogen fluoride, and this fluoride contributes as a cleaning component. In general, it is known that strict attention is required for handling hydrogen fluoride.However, in the present invention, by mixing hydrogen fluoride with a hydroxy compound or alkylamine showing basicity, Neutralized, increased in safety and easier to handle.
[0040]
(2) Chemical formula NR used in the cleaning method of the present invention ⁵ R ⁶ R ⁷ R ⁸ The hydroxy compound represented by OH is represented by the formula: ⁵ ~ R ⁸ Is a hydrogen or hydrocarbon group, but R ⁵ ~ R ⁸ At least one is a hydrogen or methyl group, and at least one is a hydrocarbon group having 2 or more carbon atoms. R ⁵ ~ R ⁸ Is defined as described above because of the aforementioned R ¹ ~ R ⁴ Is the same as
[0041]
Chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ The mixing ratio between the hydroxy compound represented by OH and hydrogen fluoride is not particularly limited. However, if the mixing ratio (hydroxy compound / hydrogen fluoride) exceeds 10 in mol ratio, the amount of hydrogen fluoride is small, so that the hydroxy compound and the hydrofluoric acid are mixed. The amount of fluoride generated by the reaction of hydrogen hydride is reduced. As a result, the detergency decreases, so that it is necessary to use a large amount of cleaning components, and accordingly, the amount of the compatibilizer used increases. For this reason, the amount of the solvent used is increased and the economy is low. From such a viewpoint, the mixing ratio is preferably set to 10 or less, and most preferably set to 1. However, if the mixing ratio is less than 1, the amount of hydrogen fluoride increases, so that handling becomes difficult. Therefore, the mixing ratio is preferably set to 0.1 or more.
[0042]
In consideration of ease of handling of hydrogen fluoride, the amount of hydrogen fluoride mixed with the high-pressure carbon dioxide fluid is preferably 0.5% by mass or less, more preferably 0.1% by mass or less. However, in the cleaning method of the present invention, the hydrogen fluoride mixed with the hydroxy compound may be in a gaseous state or a liquid state (hydrofluoric acid).
[0043]
Chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ When a hydroxy compound represented by OH and hydrogen fluoride are mixed, the chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ A fluoride represented by F is generated, and water is also generated at this time. The generation of water may also damage the Low-k film. Therefore, for a cleaning object that is easily damaged by water, the above chemical formula NR is used as a cleaning component. ¹ R ² R ³ R ⁴ It is recommended to use the fluoride denoted by F. However, the use of the above-mentioned fluoride requires a new synthesis of the fluoride, which complicates the operation. Therefore, if priority is given to the simplicity of operation, the above-mentioned chemical formula NR may be used as a cleaning component ⁵ R ⁶ R ⁷ R ⁸ It is recommended to use a mixture of a hydroxy compound represented by OH and hydrogen fluoride.
[0044]
Chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ As the hydroxy compound represented by OH, for example, benzyltrimethylammonium hydroxide, benzylcetyldimethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexyltrimethylammonium hydroxide, acetylcholine hydroxide and the like can be suitably employed.
[0045]
(3) Chemical formula NR used in the cleaning method of the present invention ⁹ R ¹⁰ R ¹¹ An alkylamine represented by the formula: ⁹ ~ R ¹¹ Is a hydrogen or hydrocarbon group, and R ⁹ ~ R ¹¹ At least one is a hydrocarbon group having 2 or more carbon atoms. R ⁹ ~ R ¹¹ Is defined as described above because of the aforementioned R ¹ ~ R ⁴ Is the same as
[0046]
Chemical formula NR ⁹ R ¹⁰ R ¹¹ The mixing ratio between the alkylamine and hydrogen fluoride represented by the formula is not particularly limited. However, if the mixing ratio (alkylamine / hydrogen fluoride) exceeds 10 in terms of mol ratio, the amount of hydrogen fluoride is small, so that The amount of fluoride generated by the reaction of hydrogen decreases. As a result, the detergency decreases, so that it is necessary to use a large amount of cleaning components, and accordingly, the amount of the compatibilizer used increases. For this reason, a large amount of solvent is required, which is not economical. From such a viewpoint, the mixing ratio is preferably set to 10 or less, and most preferably set to 1. However, if the mixing ratio is less than 1, the amount of hydrogen fluoride increases, so that handling becomes difficult. Therefore, the mixing ratio is preferably set to 0.1 or more.
[0047]
In consideration of ease of handling of hydrogen fluoride, the amount of hydrogen fluoride mixed with the high-pressure carbon dioxide fluid is preferably 0.5% by mass or less, more preferably 0.1% by mass or less. However, the hydrogen fluoride mixed with the hydroxy compound may be gaseous or liquid (hydrofluoric acid).
[0048]
Chemical formula NR ⁹ R ¹⁰ R ¹¹ As the alkylamine represented by, for example, triethylamine and tributylamine can be suitably employed.
[0049]
It is preferable that the content of the fluoride or the mixture is 0.001 to 8% by mass based on 100% by mass of the detergent composition. The above range is necessary in order to minimize the amount of the fluoride or the mixture capable of exhibiting the cleaning ability satisfactorily and the damage to the easily damaged film such as the Low-k film. If the content exceeds 8% by mass, damage to the Low-k film cannot be avoided. A more preferred upper limit is 4% by mass. In addition, the damage to the Low-k film means that the Low-k film itself is etched by the cleaning composition in the cleaning process and is reduced. The smaller the amount of the fluoride or the mixture is, the smaller the damage is. However, if not present at 0.001% by mass or more, there is a demerit that a long time is required for cleaning, so the lower limit is preferably 0.001% by mass. A more preferred lower limit is 0.005% by mass.
[0050]
The cleaning composition used in the cleaning method of the present invention contains a compatibilizer as an essential component in addition to the carbon dioxide and the cleaning component. Since the above-mentioned cleaning component is hardly dissolved in carbon dioxide, a compatibilizer is used to increase the solubility of the cleaning component in carbon dioxide. Thus, a compatibilizer is a compound that is soluble in both carbon dioxide and the fluoride or mixture.
[0051]
It is preferable to use alcohol as the compatibilizer. Alcohol is easily dissolved in carbon dioxide, and when cleaning the microstructure on which the Low-k film is formed, the alcohol protects the Low-k film, thereby suppressing the reaction between the Low-k film and the cleaning component. There is also the effect of doing. Further, alcohol has an effect of promoting the dissolution of new contaminants generated by the reaction between the low-k film and the cleaning component, and promoting the removal of polymer residues.
[0052]
Specific examples of the alcohol used as the compatibilizer include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, hexafluoroisopropanol, and the like. Among these compatibilizers, ethanol is most preferred from the viewpoint of high ability to dissolve the cleaning component in carbon dioxide.
[0053]
The compatibilizer is preferably used in an amount of 0.01 to 50% by mass based on 100% by mass of the detergent composition. In order to dissolve the washing component in carbon dioxide, the content needs to be within the above range. If the compatibilizing agent is present in an amount exceeding 50% by mass, a large amount of a solvent is required, which is not economical. A more preferred upper limit is 30% by mass. On the other hand, if not present in an amount of 0.01% by mass or more, the cleaning component cannot be dissolved in carbon dioxide, so the lower limit is preferably 0.01% by mass. A more preferred lower limit is 1% by mass.
[0054]
In order to efficiently dissolve the cleaning component in carbon dioxide, it is preferable to mix the compatibilizer about 5 times by mass the amount of the cleaning component. That is, it is recommended that the amount of the compatibilizer be adjusted within the above range according to the amount of the cleaning component.
[0055]
As described above, the cleaning composition that can be used in the cleaning method of the present invention essentially contains carbon dioxide, a cleaning component (the above-mentioned fluoride or mixture) and a compatibilizer, but impairs the object of the present invention. Other compounds (for example, propylene glycol and the like) may be contained to the extent that they are not present.
[0056]
Next, a specific method for cleaning a microstructure using the above-described cleaning composition will be described with reference to the drawings. FIG. 1 is an example of a cleaning apparatus for performing the cleaning method of the present invention. In FIG. 1, 1 is a carbon dioxide cylinder, 2 is a carbon dioxide feed pump, 3 is a cleaning component tank, 4 is a cleaning component feed pump, 5 is a switching valve, 6 is a rinse component tank, and 7 is a rinse component feed pump. , 8 is a switching valve, 9 is a high pressure vessel, 10 is a thermostat, 11 is a pressure regulating valve, and 12 is a flow meter. In FIG. 1, a method is used in which a mixture of benzyltrimethylammonium fluoride and alcohol is supplied as a cleaning component. A cleaning component tank 3 contains a mixture of benzyltrimethylammonium fluoride and alcohol in a rinse component tank. It is assumed that alcohol is stored in 6. The cleaning component tank 3 may store only benzyltrimethylammonium fluoride, and the alcohol may be separately supplied from the rinsing component tank 6 as needed.
[0057]
When the cleaning process is performed by the apparatus shown in FIG. Next, the high pressure vessel 9 is set to a predetermined temperature by the thermostatic bath 10 while the pressure is adjusted by supplying carbon dioxide from the carbon dioxide cylinder 1 to the high pressure vessel 9 by the pump 2. Note that, instead of the thermostat 10, a high-pressure vessel 9 with a heating device may be used.
[0058]
Next, a cleaning component (a mixture of benzyltrimethylammonium fluoride and alcohol) is introduced from the cleaning component tank 3 into the high-pressure vessel 9 using the pump 4 to start the cleaning process. At this time, the feeding of the carbon dioxide and the cleaning component may be performed continuously or in a batch type in which the feeding is stopped when the predetermined pressure is reached (or the feeding is stopped and circulated). But it's fine.
[0059]
The washing step is performed at 20 to 120 ° C. When the temperature is lower than 20 ° C., it takes a long time to complete the washing, and the efficiency is reduced. In the case of supercritical carbon dioxide, the temperature is set to 31 ° C. or higher. Even if the temperature exceeds 120 ° C., no improvement in cleaning efficiency is recognized, and energy is wasted. A more preferred upper limit of the temperature is 100 ° C, and a still more preferred upper limit is 80 ° C. The pressure is preferably from 5 to 30 MPa, more preferably from 7.1 to 20 MPa. The time required for cleaning may be appropriately changed depending on the size of the object to be cleaned, the amount of unnecessary substances, and the like. However, if the cleaning takes a long time, the damage of the Low-k film increases, and the cleaning is not efficient. In the case of one general wafer, the time is preferably 3 minutes or less, more preferably 2 minutes or less.
[0060]
After the cleaning, a rinsing step is performed. In the rinsing step, if the solution after cleaning in which resist residues and the like are mixed is suddenly mixed with only carbon dioxide, unnecessary substances may be precipitated, or particles generated in the cleaning step may remain on the surface of the fine structure. First, a first rinsing step using a mixture of carbon dioxide and alcohol is performed. When switching from the cleaning step to the first rinsing step, there is a possibility that the liquid composition may be changed by back mixing in the high-pressure vessel 9, but when a mixture of alcohol and carbon dioxide is used as the first rinsing liquid, this liquid composition change Since it can be reduced and the change in solubility can be reduced, inconveniences such as precipitation of cleaning components can be avoided. In this regard, it is preferable to use the same alcohol as the alcohol mixed with the cleaning component and the alcohol used in the rinsing step.
[0061]
In the first rinsing step, the supply of the cleaning component is stopped by the switching valve 5, and the switching valve 8 is opened instead, and the rinsing component (alcohol) is introduced from the rinsing component tank 6 into the high-pressure vessel 9 using the pump 7. However, the solution after washing may be discharged from the high-pressure container 9 according to the amount of introduction (the flow meter 12 may be checked). Also, during this process, the supply amount of the rinsing component (alcohol) is reduced gradually or stepwise by using the switching valve 8, and finally, only the carbon dioxide is filled in the high-pressure vessel 9 (second rinsing). Step). This is because drying is easy. The liquid derived in the washing step and the rinsing step can be separated into gaseous carbon dioxide and liquid components in the carbon dioxide recovery step consisting of, for example, a gas-liquid separation device, so that each component can be recovered and reused It is.
[0062]
After the rinsing step, when the inside of the high-pressure vessel 9 is brought to normal pressure by the pressure regulating valve 11, carbon dioxide is vaporized almost instantaneously and evaporates. Drying does not occur, and the fine pattern is not destroyed.
[0063]
1 is an example of the simplest configuration, and the configuration of the device may be changed by known means.
[0064]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are not intended to limit the present invention, and may be appropriately modified and implemented within a range that can conform to the purpose of the preceding and the following. It is possible and they are all included in the technical scope of the present invention.
[0065]
An organic silicon-based MSQ material was applied and heated on a Si wafer by a spin-on method to form an MSQ-based porous Low-k film. A pattern was formed thereon using a photoresist for ArF, and exposure and development were performed to prepare a wafer sample including a resist pattern in which lines and spaces (130 nm in width) appear alternately and a wide pattern of about 10 μm square. This wafer sample was etched with a fluorine-based gas to form a pattern on the Low-k film, and then ashing was performed with hydrogen plasma to remove the resist. When the wafer surface was observed at a magnification of 50,000 with a scanning electron microscope after the ashing process, resist residues were found on the lines on which the resist was applied and on the wide pattern. The wafer on which the resist residue was found was washed using the apparatus shown in FIG. The cleaning procedure and cleaning conditions will be described with reference to the drawings.
[0066]
Using the apparatus shown in FIG. 1, the sample after the ashing process is placed in a high-pressure vessel 9, the lid of the high-pressure vessel 9 is closed, and carbon dioxide is supplied from the carbon dioxide cylinder 1 to the high-pressure vessel 9 by the pump 2. Then, while adjusting the pressure to 15 MPa, the high-pressure vessel 9 was kept at 50 ° C. by the thermostat 10. Next, a mixture of the cleaning component and the compatibilizer to the composition shown in Table 3 was introduced from the cleaning component tank 3 into the high-pressure vessel 9 using the pump 4 so that the pressure inside the high-pressure vessel 9 became 15 MPa. The pressure control valve was opened and closed. After performing a washing step for 1 minute, and then performing a first rinsing step using the same compatibilizing agent (5% by mass) and carbon dioxide as used as the cleaning component and a second rinsing step using only oxygen dioxide, the pump 2 was turned on. After stopping, the pressure in the high-pressure container 9 was returned to normal pressure by opening the pressure regulating valve 11, and the wafer was taken out.
[0067]
In Table 3, MeOH represents methanol, EtOH represents ethanol, IPA represents isopropanol, and the amount of these compatibilizers is determined by the amount of CO in 100% by mass of the detergent composition. ₂ And the remainder other than the fluoride or mixture.
[0068]
[Table 3]

[0069]
The degree of removal of the resist residue by cleaning (cleanability), damage to the Low-k film (change in line pattern width before and after cleaning), and the cleaning component reacting with the Low-k film and the like during cleaning to cause new contamination. Whether the substance was generated or not was observed at a magnification of 50,000 with a scanning electron microscope, and the results were shown in Table 4 based on the following criteria.
[0070]
[Degree of resist residue removal (cleanability)]
○: No residue is found anywhere
Δ: Some residue is observed on either the line or the wide pattern
×: No residue was removed
[Damage of Low-k film]
：: Change in line width is less than 5% as compared to before cleaning
Δ: The change in line width was reduced by 5% or more compared to before the cleaning, but the pattern was not collapsed.
×: The etching by the cleaning component progressed too much during cleaning, and the line pattern collapsed.
[Whether new pollutants are generated]
○: No new pollutants are generated
Δ: Residue is observed on the line or wide pattern
×: Residues are observed on the line and on the wide pattern
[0071]
[Table 4]

[0072]
From Tables 3 and 4, the following can be considered. No. Nos. 1 to 17 are examples of the present invention satisfying the requirements defined in the present invention, and reliably remove unnecessary substances such as resist residues without changing the properties of the Low-k film or generating new contaminants.・ It has been removed. However, no. In No. 15, the mixing ratio between the hydroxy compound and hydrogen fluoride exceeds 10 in mol ratio, so that the detergency is slightly inferior. On the other hand, No. Nos. 18 to 21 are comparative examples that do not satisfy any of the requirements specified in the present invention, and the desired effects were not obtained.
[0073]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, when cleaning a microstructure, the fine structure which can remove and remove unnecessary substances, such as a resist residue, reliably, without changing the property of a Low-k film, or generating a new contaminant. A body washing method and a microstructure washed by the washing method can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an example of a cleaning apparatus for performing a cleaning method of the present invention.
[Explanation of symbols]
1 carbon dioxide cylinder
2 Carbon dioxide feed pump
3 Cleaning component tank
4 Cleaning component feed pump
5 Switching valve
6 alcohol tank
7 Alcohol feed pump
8 Switching valve
9 High-pressure vessel
10 constant temperature bath
11 Pressure regulating valve
12 Flow meter

Claims (7)

Carbon dioxide, a cleaning component for removing unnecessary substances, and a cleaning composition essentially including a compatibilizer for dissolving the cleaning component in the carbon dioxide, a fluid under high pressure to form a microstructure A cleaning method for removing unnecessary substances attached to the microstructure by contacting the microstructure,
A method for cleaning a microstructure, wherein a fluoride represented by a chemical formula NR ¹ R ² R ³ R ⁴ F is used as the cleaning component.
(Wherein, R ^{1 to} R ⁴ are hydrogen or a hydrocarbon group, at least one of R ^{1 to} R ⁴ is a hydrogen or a methyl group, and at least one is a hydrocarbon having 2 or more carbon atoms) Group.) Carbon dioxide, a cleaning component for removing unnecessary substances, and a cleaning composition essentially including a compatibilizer for dissolving the cleaning component in the carbon dioxide, a fluid under high pressure to form a microstructure A cleaning method for removing unnecessary substances attached to the microstructure by contacting the microstructure,
A method for cleaning a microstructure, wherein a mixture of a hydroxy compound represented by a chemical formula NR ⁵ R ⁶ R ⁷ R ⁸ OH and hydrogen fluoride is used as the cleaning component.
(Wherein, R ^{5 to} R ⁸ are a hydrogen or a hydrocarbon group, and at least one of R ^{5 to} R ⁸ is a hydrogen or a methyl group, and at least one is a hydrocarbon having 2 or more carbon atoms) Group.) Carbon dioxide, a cleaning component for removing unnecessary substances, and a cleaning composition essentially including a compatibilizer for dissolving the cleaning component in the carbon dioxide, a fluid under high pressure to form a microstructure A cleaning method for removing unnecessary substances attached to the microstructure by contacting the microstructure,
A method for cleaning a fine structure, wherein a mixture of an alkylamine represented by a chemical formula NR ⁹ R ¹⁰ R ¹¹ and hydrogen fluoride is used as the cleaning component.
(In the formula, R ^{9 to} R ¹¹ are hydrogen or a hydrocarbon group, and at least one of R ^{9 to} R ¹¹ is a hydrocarbon group having 2 or more carbon atoms.) The cleaning method according to any one of claims 1 to 3, wherein an alcohol is used as the compatibilizer. The cleaning method according to any one of claims 1 to 4, wherein the concentration of the cleaning component in the cleaning composition is 0.001 to 8% by mass. The cleaning according to any one of claims 2 to 5, wherein a mixing ratio of the hydroxy compound or the alkylamine to hydrogen fluoride (hydroxy compound or alkylamine / hydrogen fluoride) is 0.1 to 10 in a molar ratio. Method. A microstructure cleaned by the cleaning method according to claim 1.

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